A 43-year-old woman was admitted with right lower lobe pneumonia and was found to have atrial fibrillation. She had a history of bipolar disorder for which she was taking lithium. Her menstrual periods were normal.
Investigations on admission:
serum thyroid-stimulating hormone (TSH)0.98 mU/L (0.4C5.0)
serum free T428.1 pmol/L (10.0C22.0)
serum free T314.2 pmol/L (3.0C7.0)
Assay interference had been excluded.
Subsequent investigations:
serum sex hormone binding globulin64 nmol/L (40C137)
serum thyroid-hormone receptor ?-subunit0.8 IU/L (<1.0)
anti-thyroid peroxidase antibodiesnegative
What is the most likely diagnosis?
A . lithium-induced hyperthyroidism
B . non-thyroidal illness (sick euthyroid syndrome)
C . surreptitious ingestion of thyroxine
D . thyroid hormone resistance
E . TSHoma
Answer: D
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